1. Field of the Invention
The present invention pertains generally to the field of devices used for adjusting the position of the back rest in a recliner seat and more particularly is directed to an improved hydraulic positioner which is continuously self-compensating for variations in hydraulic fluid volume and visually indicates the amount of hydraulic fluid remaining in a reserve space before servicing or replacement of the unit is required.
2. State of the Prior Art
Hydraulic positioners have long been used in recliner seats where the relative position of the back rest can be fixed at a continuously adjustable angle between an upright and a reclined position. Such devices have found particularly wide application in airline passenger seating. The basic hydraulic positioner of this type has a cylinder with a piston chamber filled with a hydraulic fluid, a piston reciprocable in the chamber, and a piston rod fixed to the piston and extending through one end of the cylinder. The cylinder is fixed to the stationary bottom of the recliner seat, while the free end of the piston rod is fixed to the pivotable back rest of the recliner seat. A valve in the piston allows flow of the hydraulic fluid across the piston, but the valve is normally closed, locking the piston in place relative to the cylinder and fixing the back rest at a given position relative to the stationary bottom of the seat. If readjustment of the back rest position is desired, the valve of the hydraulic positioner is opened by means of a release actuator, such as described in U.S. Pat. No. 4,515,034 issued to this applicant, allowing fluid flow across the piston which is now free to move. After the recliner is brought to the new position, the actuating mechanism is released, returning the valve to its normal, closed position, again locking the back rest of the seat.
Existing hydraulic positioners work well and are used successfully in their intended applications, notably passenger aircraft seating. Wider application of these positioners, for example, to ground transport seating, makes desirable certain improvements. In normal use of the positioner hydraulic fluid is gradually lost over the service life of the device. In certain prior art positioners, a reserve volume of fluid is provided for replenishing the amount lost from a reservoir. An example of a prior art hydraulic positioner is described in U.S. Pat. No. 3,860,098, commonly owned with this application, where a bleed hole under a movable seal is exposed only in full extension of the positioner to replenish the piston chamber with fluid from the reservoir. Full extension occurs when the seat back is brought fully upright. To ensure regular replenishment, the seat backs in airliners are pushed to a fully upright condition between flights as part of an interior "dress-up" routine.
Compensation for thermal expansion and contraction of the hydraulic fluid is specially significant in ground transport applications, where hydraulic positioners may be subject to a very wide thermal range, varying with the local climate and the seasons. Contraction of the hydraulic fluid exposed to cold temperatures can create a vacuum space in the piston chamber which in turn allows a degree of free movement to the piston. Conventional hydraulic locks compensate for this condition when the seat back is brought upright. Failure to do so, however, results in a floppy condition of the seat back with the hydraulic positioner locked. It is also desirable to continously compensate for the change in effective piston chamber volume which occurs as the piston rod moves in and out of the chamber during the stroke of the piston. As the rod is withdrawn, the effective volume of the piston chamber increases by the volume of the rod segment withdrawn from the chamber. This condition can also create a vacuum space in the piston chamber, which unless compensated by replenishment from a reservoir of hydraulic fluid, may likewise creates a floppy condition of the seat back. These characteristics of prior art devices have no significant impact, however, in applications where professional maintenance crews regularly and frequently return the seat backs to a vertical condition, and where the operating temperature range is relatively limited. Owners of private vehicles, on the other hand, cannot be relied upon to return the seat to a fully upright position with any regularity to replenish fluid lost from the piston chamber.
Prior art hydraulic positioners lack an easy indication of the hydraulic fluid remaining in the device. The service life of a given unit ends after the hydraulic fluid in the reservoir is exhausted and an appreciable amount of fluid is lost from the piston chamber. Under these conditions, replenishment no longer occurs, resulting in an increasingly severe flop of the seat back due to the growing void space in the piston chamber. In existing devices maintenance crews receive no advance warning that would enable preventive replacement of the device before performance deteriorates significantly.
The present trend in ground transport applications is to use gas-spring positioners. These devices are low cost, but have poor service life because of leakage of their highly compressed gas charge. Hydraulic positioners offer many advantages over gas-spring devices. However, wider usage of hydraulic positioners in such applications calls for a low cost hydraulic positioner which is continuously self compensating for changes in piston chamber volume due to piston rod movement, for changes in hydraulic fluid volume resulting from thermal expansion/contraction, and for fluid loss over the service life of the device, without having to bring the device to full extension for replenishment of fluid to occur. A further need exists for a hydraulic positioner with external visual indication of the remaining volume of reserve hydraulic fluid to make possible preventive replacement of nearly exhausted units.